This invention relates to an apparatus and method for measuring reaction forces and weight shifts. More particularly, this invention relates to an apparatus and method for measuring vertical ground reaction forces and weight shifts produced by a golfer during a golf swing.
As is known, various techniques have been employed for measuring and analyzing the vertical ground reaction forces produced during the swing of a golfer. This data has been used for the following purposes; 1) to understand the interaction forces between the ground and the golfer during a swing, 2) to provide a method of comparison between golfers in order to analyze and/or adjust the swing to some type of ideal swing, and 3) to provide relevant data for the design and evaluation of golf equipment.
For example, in a copending application, there is a description of a motion analysis system and associated computer model for analyzing a golf swing which is able to measure the vertical ground reaction forces caused by a golfer during a swing in order to serve as a control for the analysis operation of the computer model.
As is known by golfers and those who instruct in golf, there is a considerable shifting of weight during a swing even though there is no change in the overall position of the feet. For example, a purposeful shifting of the weight between the feet must occur in order to generate maximum swing power. Also, local weight shifting through foot movements in both the heel-to-toe and outside-to-instep directions is an important component of the overall golf swing. Providing this information in addition to measured ground reaction forces would improve the ability to meet the objectives mentioned above.
However, it has not been known that any attempt has been made to configure a device that simultaneously measures the vertical ground reaction forces, foot-to-foot weight shifts, and local weight shifts from foot movements, for example, from heel-to-toe and/or from outside-to-instep, during a golf swing.
Accordingly, it is an object of the invention to provide a method of accurately measuring the foot-to-foot weight shifts during a golf swing.
It is another object of this invention to provide a method of accurately measuring heel-to-toe weight shifts during a golf swing.
It is another object of this invention to provide a method of accurately measuring outside-to-instep weight shifts during a golf swing.
It is another object of this invention to be able to combine the ability to accurately measure weight shifts with the ability to accurately measure the vertical reaction forces during a golf swing.
It is another object of this invention to be able to measure the rate of change of vertical reaction forces and foot-to-foot, heel-to-toe, and outside-to-instep weight shifts over time during a golf swing.
It is another object of this invention to provide an analytical method of evaluating golf swings using reaction force and weight shift information.
It is another object of this invention to analyze a golf swing using synchronized foot force and video data.
It is another object of this invention that the system be easy to operate, unobtrusive to the golfer, and provide quick and meaningful feedback.
It is another object of the invention to be able to compare golf swings based upon reaction force and weight shift characteristics.
It is another object of the invention to be able to evaluate golf equipment based upon the reaction force and weight shift characteristics of a golfer.
It is another object of the invention to comprehensively analyze the biomechanics of a golf swing and the effects of equipment on a golfer.
Briefly, the invention provides an apparatus for measuring vertical ground reaction forces which comprises a pair of force plates upon which a golfer is positioned during a golf swing. Each force plate is constructed to react not only to the downward forces of a golfer but also to shifts in the golfer""s weight. To this end, each force plate has a rigid frame, a pair of beams mounted on the frame in cantilevered manner at each of two opposite sides of the frame with each pair of beams extending from one side of the frame toward the opposite side of the frame. In addition, a plurality of ball bearings are provided with each ball bearing disposed on a free end of a respective beam while a plate is mounted on the ball bearings and extends over the beams so as to receive a load, for example, the foot of a golfer. The construction of each foot plate is such that a downward load on the plate causes the beams to deflect.
The apparatus also includes sensing means adjacent each beam for sensing a deflection of the beam and for emitting a voltage signal indicative of the sensed deflection. This sensing means may be in the form of strain gauges for measuring the deflection of a beam under a load. In a preferred embodiment, a pair of strain gauges are disposed at each beam with one strain gauge disposed below the beam and the other strain gauge disposed above the beam arranged such that they measure temperature insensitive deflection.
The apparatus also employs a processing unit which is connected to the sensing means to receive voltage signals therefrom in order to calculate reaction forces corresponding thereto. This processing unit includes a data acquisition board which is connected to each sensing means for receiving the voltage signals. The board also includes a plurality of analog/digital converters for transforming the voltage signals into binary numbers and a BASIC program connected with the converters to calibrate the binary numbers to reaction forces. The processing unit also includes a means to process the beam reaction force data to determine total vertical reaction forces, foot-to-foot weight shift, heel-to-toe weight shift, and outside-to-instep weight shift. The processing unit also includes a means to determine the speed at which the vertical reaction forces and weight shifts take place.
Still further, the apparatus includes a monitor which is connected to the processing unit for graphically displaying combinations of the beam reaction forces per unit of time to visually indicate at least one of a total vertical reaction force of the golfer, foot-to-foot weight shift of the golfer between the two plates, a heel-to-toe weight shift of the golfer""s feet, and an outside-to-instep weight shift of the golfer""s feet over time.
For example, the monitor may be used for graphically displaying the sum of the beam reaction forces of each force plate per unit of time in order to visually indicate a foot-to-foot weight shift over time between the two foot plates.
The monitor may also be used to graphically display a quantity indicative of the movement of the location of the vertical reaction force in the heel-to-toe direction as sensed by the difference in the sum of the beam reaction forces of one pair of beams relative to the opposite pair of beams of each foot plate so as to visually indicate a heel-to-toe weight shift on each foot plate over time.
Likewise, the monitor may be used to graphically display a quantity indicative of the movement of the location of the vertical reaction force in the outside-to-instep direction as sensed by the difference in the sum of the beam reaction forces on one pair of opposed beams relative to the other pair of opposed beams of each foot plate per unit of time to visually indicate an outside-to-instep weight shift on each foot plate over time.
The invention also provides a method of measuring ground reaction forces in the vertical direction during a golf swing. In this regard, the method includes the step of positioning a golfer on a pair of plates wherein each plate is supported at two pairs of points at opposite ends of the plate to transfer the weight of a golfer""s foot thereto during a golf swing. The points of support may be defined as movable points, such as a point on the free end of a cantilevered beam. In accordance with the method, the movement or deflection of each point is sensed during a golf swing and a vertical reaction force for each point corresponding to the deflection is calculated.
In accordance with the invention, a graphic display is made of combinations of the beam reaction forces per unit of time to visually indicate at least one of a total vertical reaction force of the golfer, foot-to-foot weight shift of the golfer, the heel-to-toe weight shift of the golfer on each plate, and an outside-to-instep weight shift of the golfer on each plate over time. Still further, the rate of change of a respective one of the reaction forces and weight shifts over time may also be graphically plotted.